Some electrical and pharmacological properties of gap junctions between adult ventricular myocytes

1985 ◽  
Vol 249 (5) ◽  
pp. C447-C455 ◽  
Author(s):  
R. L. White ◽  
D. C. Spray ◽  
A. C. Campos de Carvalho ◽  
B. A. Wittenberg ◽  
M. V. Bennett
Keyword(s):  
Gap Junctions ◽  
Cardiac Tissue ◽  
Ventricular Myocytes ◽  
Input Resistance ◽  
Adult Rat ◽  
Junctional Communication ◽  
Cell Tissue ◽  
Physiological Properties ◽  
Rat Hearts ◽  
Junctional Conductance

Ventricular myocytes were isolated from adult rat hearts using the technique of Wittenberg and Robinson (Cell Tissue Res. 216: 231-251, 1981). These cells exhibited morphology, input resistance, time constant, and excitability expected for cells in intact cardiac tissue. Pairs of these cells were electronically coupled, and junctional conductance was unaffected by transjunctional potential or hyperpolarization of both cells. Brief exposure of cell pairs to medium equilibrated with 100% CO2 or containing 0.1 mM octanol quickly and reversibly decreased junctional conductance. We conclude that gap junctions between pairs of ventricular myocytes possess physiological properties like those of junctions in many other tissues. This preparation will be useful in evaluating drug action on junctional communication in heart.

Regulation of gap junctional conductance

1985 ◽  
Vol 248 (6) ◽  
pp. H753-H764 ◽  
Author(s):  
D. C. Spray ◽  
R. L. White ◽  
F. Mazet ◽  
M. V. Bennett
Keyword(s):  
Gap Junctions ◽  
Ventricular Myocytes ◽  
Cross Reactivity ◽  
Cardiac Cells ◽  
Rat Ventricular Myocytes ◽  
Gating Mechanisms ◽  
Conduction Disorders ◽  
Wide Range ◽  
Junctional Conductance ◽  
Gap Junctional

Gap junctional conductance is regulated by the number of channels between coupled cells (the balance between formation and loss of these channels) and by the fraction of these channels that are open (gating mechanisms). A variety of treatments are known to affect junction formation. Adenosine 3',5'-cyclic monophosphate (cAMP) is involved in some cases, and protein synthesis may be required but precursor molecules can also exist. Junction removal occurs both by dispersion of particles and by internalization of junctional membrane. Factors promoting removal are not well understood. A variety of gating mechanisms exist. Coupling may be controlled by changes in conductance of nonjunctional membranes. Several kinds of voltage dependence of junctional conductance are known, but rat ventricular junctions at least are electrically linear. Cytoplasmic acidification decreases conductance of most gap junctions. Sensitivity in rat ventricular myocytes allows modulation of coupling by moderate changes near normal internal pH. Increasing intracellular Ca also decreases junctional conductance, but in the better studied cases sensitivity is much lower to Ca than H. A few data support low sensitivity to Ca in cardiac cells, but quantitative studies are lacking. Higher alcohols such as octanol block junctional conductance in a wide range of tissues including rat ventricular myocytes. An antibody to liver gap junctions blocks junctions between rat ventricular myocytes. Cross reactivity indicates at least partial homology between many gap junctions. Although differences among gap junctions are known, a general physiology is being developed, which may have considerable relevance to normal cardiac function and also to conduction disorders of that tissue.

Propofol Increases Contractility during α1a-Adrenoreceptor Activation in Adult Rat Cardiomyocytes

2005 ◽  
Vol 103 (2) ◽  
pp. 335-343 ◽  
Author(s):  
Brad D. Gable ◽  
Toshiya Shiga ◽  
Paul A. Murray ◽  
Derek S. Damron
Keyword(s):  
Phospholipase A2 ◽  
Ventricular Myocytes ◽  
Rho Kinase ◽  
Selective Inhibition ◽  
Rat Cardiomyocytes ◽  
Adult Rat ◽  
Kinase C ◽  
Rat Hearts ◽  
Dependent Pathway ◽  
Exchange Activity

Background The objective of this study was to identify the extent to which propofol alters intracellular free Ca2+ concentration ([Ca2+]i), myofilament Ca sensitivity, and contraction of individual cardiomyocytes during activation of alpha1a adrenoreceptors and to determine the cellular mechanism of action. Methods Freshly isolated ventricular myocytes were obtained from adult rat hearts. Myocyte shortening and [Ca2+]i were simultaneously monitored in individual cardiomyocytes exposed to phenylephrine after treatment with chloroethylclonidine (alpha1b-adrenoreceptor antagonist) and BMY 7378 (alpha1d-adrenoreceptor antagonist). Data are reported as mean +/- SD. Results Phenylephrine increased myocyte shortening by 124 +/- 9% (P = 0.002), whereas peak [Ca2+]i only increased by 8 +/- 3% (P = 0.110). Inhibition of phospholipase A2 and phospholipase C attenuated the phenylephrine-induced increase in shortening by 84 +/- 11% (P = 0.004) and 15 +/- 6% (P = 0.010), respectively. Inhibition of protein kinase C (PKC) and Rho kinase attenuated the phenylephrine-induced increase in shortening by 17 +/- 8% (P = 0.010) and 74 +/- 13% (P = 0.006), respectively. In the presence of phenylephrine, propofol increased shortening by 40 +/- 6% (P = 0.002), with no concomitant increase in [Ca2+]i. PKC inhibition prevented the propofol-induced increase in shortening. Selective inhibition of PKCalpha, PKCdelta, PKCepsilon, and PKCzeta reduced the propofol-induced increase in shortening by 12 +/- 5% (P = 0.011), 36 +/- 8% (P = 0.001), 32 +/- 9% (P = 0.007), and 19 +/- 5% (P = 0.008), respectively. Na+ - H+ exchange inhibition reduced the propofol-induced increase in shortening by 56 +/- 7% (P = 0.001). Conclusion Activation of alpha1a adrenoreceptors increases cardiomyocyte shortening primarily via a phospholipase A2-dependent, Rho kinase-dependent increase in myofilament Ca2+ sensitivity. Propofol further increases myofilament Ca2+ sensitivity and shortening via a PKC-dependent pathway and an increase in Na+ - H+ exchange activity.

Characterization of stimulation of phosphoinositide hydrolysis by alpha 1-adrenergic agonists in adult rat hearts

1994 ◽  
Vol 267 (3) ◽  
pp. H970-H978 ◽  
Author(s):  
A. Lazou ◽  
S. J. Fuller ◽  
M. A. Bogoyevitch ◽  
K. A. Orfali ◽  
P. H. Sugden
Keyword(s):  
Ventricular Myocytes ◽  
Irreversible Inhibitor ◽  
Adult Rat ◽  
Fixed Concentration ◽  
Rat Hearts ◽  
Site Competition ◽  
Pi Hydrolysis ◽  
Hydrolysis Of ◽  
Stimulation Of

The coupling of the pharmacologically defined alpha 1A- and alpha 1B-adrenoceptors to the hydrolysis of phospho[3H]inositides (PI) was investigated in ventricular myocytes freshly isolated from adult rat hearts. The alpha 1-adrenoceptor population in the heart was characterized by competitive binding experiments using [3H]prazosin and the alpha 1A-adrenoceptor-selective antagonist 5-methyl urapidil. It was heterogeneous with approximately 25% being pharmacologically of the alpha 1A-adrenoceptor subtype and 75% being of the alpha 1B-adrenoceptor subtype. Epinephrine, norepinephrine, or phenylephrine stimulated PI hydrolysis in the presence or absence of propranolol. The greatest stimulation (7-fold) was with epinephrine. The half-maximum effective concentrations for agonists were approximately 0.5-3.5 and 0.2 microM in the absence and presence of propranolol, respectively. The inhibition by 5-methyl urapidil of the stimulation of PI hydrolysis by a fixed concentration of epinephrine fitted a two-site competition curve. The distribution between high-affinity (25%) and low-affinity (75%) sites suggested that both the alpha 1A- and alpha 1B-adrenoceptors were coupled to PI hydrolysis in proportion to their relative abundance. Equally, the stimulation of PI hydrolysis by epinephrine in the presence of a fixed concentration of 5-methyl urapidil was biphasic. In addition, chloroethylclonidine, an irreversible inhibitor of the alpha 1B-adrenoceptor, inhibited the epinephrine stimulation of PI hydrolysis by 35%. We conclude that the pharmacologically defined alpha 1A- and alpha 1B-adrenoceptor subtypes are both coupled to PI hydrolysis in the ventricular myocyte.

scholarly journals Dynamic model for ventricular junctional conductance during the cardiac action potential

2005 ◽  
Vol 288 (3) ◽  
pp. H1113-H1123 ◽  
Author(s):  
Xianming Lin ◽  
Joanna Gemel ◽  
Eric C. Beyer ◽  
Richard D. Veenstra
Keyword(s):  
Action Potential ◽  
Gap Junctions ◽  
Gap Junction ◽  
Ventricular Myocytes ◽  
Conduction Block ◽  
Gap Junction Channels ◽  
Dependent Inactivation ◽  
Junctional Conductance ◽  
Triggered Arrhythmias ◽  
Cx 43

The ventricular action potential was applied to paired neonatal murine ventricular myocytes in the dual whole cell configuration. During peak action potential voltages >100 mV, junctional conductance ( gj) declined by 50%. This transjunctional voltage ( Vj)-dependent inactivation exhibited two time constants that became progressively faster with increasing Vj. Gj returned to initial peak values during action potential repolarization and even exceeded peak gj values during the final 5% of repolarization. This facilitation of gj was observed <30 mV during linearly decreasing Vj ramps. The same behavior was observed in ensemble averages of individual gap junction channels with unitary conductances of 100 pS or lower. Immunohistochemical fluorescent micrographs and immunoblots detect prominent amounts of connexin (Cx)43 and lesser amounts of Cx40 and Cx45 proteins in cultured ventricular myocytes. The time dependence of the gj curves and channel conductances are consistent with the properties of predominantly homomeric Cx43 gap junction channels. A mathematical model depicting two inactivation and two recovery phases accurately predicts the ventricular gj curves at different rates of stimulation and repolarization. Functional differences are apparent between ventricular myocytes and Cx43-transfected N2a cell gap junctions that may result from posttranslational modification. These observations suggest that gap junctions may play a role in the development of conduction block and the genesis and propagation of triggered arrhythmias under conditions of slowed conduction (<10 cm/s).

The effect of adrenomedullin on the L-type calcium current in myocytes from septic shock rats: signaling pathway

2007 ◽  
Vol 293 (5) ◽  
pp. H2888-H2893 ◽  
Author(s):  
Xiao-Hui Zhang ◽  
Gui-Rong Li ◽  
Jean-Pierre Bourreau
Keyword(s):  
Septic Shock ◽  
Calcium Current ◽  
Cardiac Tissue ◽  
Ventricular Myocytes ◽  
Adult Rats ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Mediated Effects ◽  
Whole Cell Patch Clamp ◽  
Cox 2

Adrenomedullin (ADM) is upregulated in cardiac tissue under various pathophysiological conditions, particularly in septic shock. The intracellular mechanisms involved in the effect of ADM on adult rat ventricular myocytes are still to be elucidated. Ventricular myocytes were isolated from adult rats 4 h after an intraperitoneal injection of lipopolysaccharide (LPS, 10 mg/kg). Membrane potential and L-type calcium current ( ICa,L) were determined using whole cell patch-clamp methods. APD in LPS group was significantly shorter than control values (time to 50% repolarization: LPS, 169 ± 2 ms; control, 257 ± 2 ms, P < 0.05; time to 90% repolarization: LPS, 220 ± 2 ms; control, 305 ± 2 ms, P < 0.05). ICa,L density was significantly reduced in myocytes from the LPS group (−3.2 ± 0.8 pA/pF) compared with that of control myocytes (−6.7 ± 0.3 pA/pF, P < 0.05). The ADM antagonist ADM-(22-52) reversed the shortened APD and abolished the reduction of ICa,L in shock myocytes. In myocytes from control rats, incubating with ADM for 1 h induced a marked decrease in peak ICa,L density. This effect was reversed by ADM-(22-52). The Gi protein inhibitor, pertussis toxin (PTX), the protein kinase A (PKA) inhibitor, KT-5720, and the specific cyclooxygenase 2 (COX-2) inhibitor, nimesulide, reversed the LPS-induced reduction in peak ICa,L. The results suggest a COX-2-involved PKA-dependent switch from Gs coupled to PTX-sensitive Gi coupling by ADM in adult rat ventricular myocytes. The present study delineates the intracellular pathways involved in ADM-mediated effects on ICa,L in adult rat ventricular myocytes and also suggests a role of ADM in sepsis.

scholarly journals Increased susceptibility of aged hearts to ventricular fibrillation during oxidative stress

2009 ◽  
Vol 297 (5) ◽  
pp. H1594-H1605 ◽  
Author(s):  
Norishige Morita ◽  
Ali A. Sovari ◽  
Yuanfang Xie ◽  
Michael C. Fishbein ◽  
William J. Mandel ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Young Adult ◽  
Ventricular Myocytes ◽  
Tissue Level ◽  
Left Ventricular ◽  
Middle Aged ◽  
Aged Rat ◽  
Adult Rat ◽  
Inactive Form ◽  
Rat Hearts

Oxidative stress with hydrogen peroxide (H2O2) readily promotes early afterdepolarizations (EADs) and triggered activity (TA) in isolated rat and rabbit ventricular myocytes. Here we examined the effects of H2O2 on arrhythmias in intact Langendorff rat and rabbit hearts using dual-membrane voltage and intracellular calcium optical mapping and glass microelectrode recordings. Young adult rat (3–5 mo, N = 25) and rabbit (3–5 mo, N = 6) hearts exhibited no arrhythmias when perfused with H2O2 (0.1–2 mM) for up to 3 h. However, in 33 out of 35 (94%) aged (24–26 mo) rat hearts, 0.1 mM H2O2 caused EAD-mediated TA, leading to ventricular tachycardia (VT) and fibrillation (VF). Aged rabbits (life span, 8–12 yr) were not available, but 4 of 10 middle-aged rabbits (3–5 yr) developed EADs, TA, VT, and VF. These arrhythmias were suppressed by the reducing agent N-acetylcysteine (2 mM) and CaMKII inhibitor KN-93 (1 μM) but not by its inactive form (KN-92, 1 μM). There were no significant differences between action potential duration (APD) or APD restitution slope before or after H2O2 in aged or young adult rat hearts. In histological sections, however, trichrome staining revealed that aged rat hearts exhibited extensive fibrosis, ranging from 10–90%; middle-aged rabbit hearts had less fibrosis (5–35%), whereas young adult rat and rabbit hearts had <4% fibrosis. In aged rat hearts, EADs and TA arose most frequently (70%) from the left ventricular base where fibrosis was intermediate (∼30%). Computer simulations in two-dimensional tissue incorporating variable degrees of fibrosis showed that intermediate (but not mild or severe) fibrosis promoted EADs and TA. We conclude that in aged ventricles exposed to oxidative stress, fibrosis facilitates the ability of cellular EADs to emerge and generate TA, VT, and VF at the tissue level.

Expression and regulation of connexins in cultured ventricular myocytes isolated from adult rat hearts

2002 ◽  
Vol 443 (5) ◽  
pp. 676-689 ◽  
Author(s):  
Lioudmila O. Polontchouk ◽  
Virginijus Valiunas ◽  
Jacques-Antoine Haefliger ◽  
Hans M. Eppenberger ◽  
Robert Weingart
Keyword(s):  
Ventricular Myocytes ◽  
Adult Rat ◽  
Rat Hearts

Iron storage sites in the myocardium as revealed by cytohistochemistry

1988 ◽  
Vol 46 ◽  
pp. 394-395
Author(s):  
M. Ashraf ◽  
F. Thompson ◽  
S. Miki ◽  
P. Srivastava
Keyword(s):  
Cardiac Tissue ◽  
Coronary Perfusion ◽  
Intracellular Iron ◽  
Ether Anesthesia ◽  
Intense Staining ◽  
Iron Storage ◽  
Thin Sections ◽  
Rat Hearts ◽  
Cacodylate Buffer ◽  
Made In

Iron is believed to play an important role in the pathogenesis of ischemic injury. However, the sources of intracellular iron in myocytes are not yet defined. In this study we have attempted to localize iron at various cellular sites of the cardiac tissue with the ferrocyanide technique.Rat hearts were excised under ether anesthesia. They were fixed with coronary perfusion with 3% buffered glutaraldehyde made in 0.1 M cacodylate buffer pH 7.3. Sections, 60 μm in thickness, were cut on a vibratome and were incubated in the medium containing 500 mg of potassium ferrocyanide in 49.5 ml H2O and 0.5 ml concentrated HC1 for 30 minutes at room temperature. Following rinses in the buffer, tissues were dehydrated in ethanol and embedded in Spurr medium.The examination of thin sections revealed intense staining or reaction product in peroxisomes (Fig. 1).

Load-Induced Growth Responses in Isolated Adult Rat Hearts

Circulation ◽  
1997 ◽  
Vol 95 (12) ◽  
pp. 2677-2683 ◽  
Author(s):  
Christiane D. Thienelt ◽  
Ellen O. Weinberg ◽  
Jozef Bartunek ◽  
Beverly H. Lorell
Keyword(s):  
Growth Responses ◽  
Adult Rat ◽  
Rat Hearts

scholarly journals Effects of acidosis on resting cytosolic and mitochondrial Ca2+ in mammalian myocardium.

1993 ◽  
Vol 102 (3) ◽  
pp. 575-597 ◽  
Author(s):  
G Gambassi ◽  
R G Hansford ◽  
S J Sollott ◽  
B A Hogue ◽  
E G Lakatta ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Ventricular Myocytes ◽  
Free Acid ◽  
Left Ventricular ◽  
Ruthenium Red ◽  
Acetoxymethyl Ester ◽  
Cytosolic Ph ◽  
Bicarbonate Buffer ◽  
Adult Rat ◽  
Mammalian Myocardium

Acidosis increases resting cytosolic [Ca2+], (Cai) of myocardial preparations; however, neither the Ca2+ sources for the increase in Cai nor the effect of acidosis on mitochondrial free [Ca2+], (Cam) have been characterized. In this study cytosolic pH (pHi) was monitored in adult rat left ventricular myocytes loaded with the acetoxymethyl ester (AM form) of SNARF-1. A stable decrease in the pHi of 0.52 +/- 0.05 U (n = 16) was obtained by switching from a bicarbonate buffer equilibrated with 5% CO2 to a buffer equilibrated with 20% CO2. Electrical stimulation at either 0.5 or 1.5 Hz had no effect on pHi in 5% CO2, nor did it affect the magnitude of pHi decrease in response to hypercarbic acidosis. Cai was measured in myocytes loaded with indo-1/free acid and Cam was monitored in cells loaded with indo-1/AM after quenching cytosolic indo-1 fluorescence with MnCl2. In quiescent intact myocytes bathed in 1.5 mM [Ca2+], hypercarbia increased Cai from 130 +/- 5 to 221 +/- 13 nM. However, when acidosis was effected in electrically stimulated myocytes, diastolic Cai increased more than resting Cai in quiescent myocytes, and during pacing at 1.5 Hz diastolic Cai was higher (285 +/- 17 nM) than at 0.5 Hz (245 +/- 18 nM; P &lt; 0.05). The magnitude of Cai increase in quiescent myocytes was not affected either by sarcoplasmic reticulum (SR) Ca2+ depletion with ryanodine or by SR Ca2+ depletion and concomitant superfusion with a Ca(2+)-free buffer. In unstimulated intact myocytes hypercarbia increased Cam from 95 +/- 12 to 147 +/- 19 nM and this response was not modified either by ryanodine and a Ca(2+)-free buffer or by 50 microM ruthenium red in order to block the mitochondrial uniporter. In mitochondrial suspensions loaded either with BCECF/AM or indo-1/AM, acidosis produced by lactic acid addition decreased both intra- and extramitochondrial pH and increased Cam. Studies of mitochondrial suspensions bathed in indo-1/free acid-containing solution showed an increase in extramitochondrial Ca2+ after the addition of lactic acid. Thus, in quiescent myocytes, cytoplasmic and intramitochondrial buffers, rather than transsarcolemmal Ca2+ influx or SR Ca2+ release, are the likely Ca2+ sources for the increase in Cai and Cam, respectively; additionally, Ca2+ efflux from the mitochondria may contribute to the raise in Cai. In contrast, in response to acidosis, diastolic Cai in electrically stimulated myocytes increases more than resting Cai in quiescent cells; this suggests that during pacing, net cell Ca2+ gain contributes to enhance diastolic Cai.

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